Conventionally, a plasma processing apparatus using a radial line slot antenna has been known as a plasma processing apparatus that performs a predetermined plasma processing on an object to be processed such as, for example, a semiconductor wafer. The radial line slot antenna is disposed in such a manner that a slot plate with a plurality of slots is disposed in a state where a slow wave plate is laid on the slot plate above a dielectric window disposed in a ceiling opening of a processing container, and the slot plate is connected to a coaxial waveguide at the central portion thereof. With such a configuration, microwaves generated by a microwave generator pass through the coaxial waveguide. Then, the microwaves are radially transferred in the radial direction by the slow wave plate via the coaxial waveguide to generate circularly polarized waves by the slot plate, and then, radiated from the slot plate into the processing container through the dielectric window. Then, high density plasma having a low electron temperature may be generated by the microwaves within the processing container under a low pressure, and a plasma processing such as, for example, a film forming processing or an etching processing, may be performed by the generated plasma.
In order to perform the plasma processing uniformly, it is necessary to make the plasma distribution within the processing container uniform. Thus, in the plasma processing apparatus disclosed in Japanese Patent No. 3787297, it is proposed to periodically form uneven portions, which consist of protrusions, at a pitch of 7.5 mm to 30 mm on the processing container side surface of the dielectric window. In such a case, according to the periodic existence of the uneven portions, generation of surface waves, which are resonant with an electron density, is suppressed, and plasma is generated in which the electron density is not extremely changed regardless of whether the microwave power is large or small. In addition, it is ensured that stable plasma is generated within the processing container.